MPI_FILE_WRITE_ORDERED(3)

💖 MPI_File_write_ordered 💖

okay bestie, welcome to the Open MPI manual, section 3 — this is the MPI_File_write_ordered page and it's literally about writing to a file at a location that the shared file pointer picks out. Blocking. Collective. Very demure, very mindful. ✨

MPI_File_write_ordered — Writes a file at a location specified by a shared file pointer (blocking, collective).

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🌸 SYNTAX 🌸

✨ C Syntax

#include <mpi.h>

int MPI_File_write_ordered(MPI_File fh, const void *buf,
    int count, MPI_Datatype datatype,
    MPI_Status *status)

✨ Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_FILE_WRITE_ORDERED(FH, BUF, COUNT, DATATYPE,
    STATUS, IERROR)
    <type>  BUF(*)
    INTEGER FH, COUNT, DATATYPE, STATUS(MPI_STATUS_SIZE), IERROR

✨ Fortran 2008 Syntax

USE mpi_f08

MPI_File_write_ordered(fh, buf, count, datatype, status, ierror)
    TYPE(MPI_File), INTENT(IN) :: fh
    TYPE(*), DIMENSION(..), INTENT(IN) :: buf
    INTEGER, INTENT(IN) :: count
    TYPE(MPI_Datatype), INTENT(IN) :: datatype
    TYPE(MPI_Status) :: status
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🎀 INPUT PARAMETERS 🎀

• fh — the File handle (a handle, bestie). 🗂️
• buf — initial address of the buffer (a choice, iykyk). 📮
• count — how many elements are chillin' in that buffer (an integer). 🔢
• datatype — the data type of each buffer element (a handle). 🏷️

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🦋 OUTPUT PARAMETERS 🦋

• status — Status object (a Status, iconic). 📋
• ierror — Fortran only: error status (an integer). 🚨

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🌈 DESCRIPTION 🌈

okay so MPI_File_write_ordered is a collective routine, no cap. That means every single process in the communicator group associated with the file handle fh has to call it. Everyone. Together. Group chat rules. 💅

Each process is allowed to pass different argument values for the datatype and count arguments — so like, nobody has to match, it's giving individuality. ✨

Every process attempts to write, into the file associated with fh, a total number of count data items having datatype type contained in the user's buffer buf. 🫶

For each process, the location in the file where the data gets written is the position at which the shared file pointer would be after all processes whose ranks within the group are less than that of this process had written their data. Yeah. Rank order = write order. Main character energy, in line. 👑

MPI_File_write_ordered returns the number of datatype elements written in status. 📊

And the shared file pointer gets updated by the amounts of data requested by all processes of the group. Everyone pitched in, everyone moves the pointer. periodt. 🌟

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💀 ERRORS 💀

ngl bestie, basically almost all MPI routines return an error value: C routines as the return result of the function, and Fortran routines in the last argument. 🫠

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init / MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn / MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions. 😭

Open MPI ships with three predefined error handlers you can use:

• MPI_ERRORS_ARE_FATAL — Causes the program to abort all connected MPI processes. 🔥
• MPI_ERRORS_ABORT — An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process. 💥
• MPI_ERRORS_RETURN — Returns an error code to the application. 📬

MPI applications can also implement their own error handlers by calling:

• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler

⚠️ Note that MPI does not guarantee that an MPI program can continue past an error. like, it might just be over. 🙈

See the MPI man page for a full list of MPI error codes. 📖

See the Error Handling section of the MPI-3.1 standard for more information. 📚

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👑 Copyright 👑

2003-2026, The Open MPI Community

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and that's the whole page, bestie! 🎀 this little manual entry dropped on Sep 10, 2026, straight from the Open MPI girlies, and it's filed under MPI_FILE_WRITE_ORDERED(3) in section 3. slay, go write something ordered. 💜🌸